The present invention relates to coated gall-resistant surgical saw blades. Orthopedic surgeons utilize saw blades of various shapes and configurations in the performance of surgical procedures. One such saw blade is known as a reciprocating saw blade and is designed to interact with a precision slot which guides the saw blade in reciprocating movements to cut bone tissue during the performance of surgery.
Customarily, a reciprocating surgical blade has a plurality of teeth on each of its two edges. These teeth are customarily provided in a set, that is, consecutive teeth are bent in alternate directions. As this set is provided on known surgical saw blades, the ends of the teeth extend upwardly and downwardly beyond the respective planes of the respective side faces of the blade. Thus, often, it is these ends of the teeth which guide the saw blade within the precision slot. Of course, inherently, this causes wear of the teeth quite prematurely and results in the surgeon having to change saw blades quite often during the surgical case.
Another type of saw blade is known as a sagittal saw blade and consists of a flat elongated blade with a proximal saw engaging slot and a distal transverse surface having a plurality of teeth thereon, with the teeth being flat in configuration, that is, not provided in a set.
There are but two examples of surgical saw blades which may form a part of the present invention.
Studies have been conducted on the effect on bone tissue of blades which have been galled for whatever reason. In an article titled "Orthopedic Saw Blades A Case Study" by H. W. Wevers, et al., published in the journal of Arthroplasty, Volume 2 No. 1, Mar. 1987, this problem is discussed. The following is quoted from this article: "Because these blades are used primarily for total knee arthroplasty, it is probable that the damage occurred from direct contact of the cutting edges with metal templates or instruments used in the operation. This type of damage had a direct influence on the mechanical work needed to operate the saw." Later in the publication, the following is stated: "Excessive heat induces thermal damage to osteocytes and expands the zone of necrosis beyond that shown microscopically." Further, the following is stated: "Smooth, accurately cut surfaces are recognized as an important factor for bone ingrowth into porous-coated prostheses. Such clean bone cuts enhance prosthetic fit and setting, therefore promoting an even load bearing to the bone, and improved alignment of the prostheses or osteotomies." Finally, the following is stated: "Damage to blade cutting surfaces due to inadvertent contact with templates and instruments may be unavoidable with currently available techniques."
A publication titled "Avoiding thermal damage to bone: Machining principals applied to powered bone surgery, a literature review", by Ray Umber, et al. further discusses the problems attendant in the prior art. The following is disclosed therein: "Thus, cutting with a dull tool, increases the amount of frictional heat generated, much of which is now located in the workpiece itself. With a dull tool not only is the surface of the workpiece increasing in temperature but also the cut is no longer clean."
A further problem with prior art saw blades is also set forth in this publication. In particular, prior art saw blades are so designed that it is difficult to provide water to the site of the operation for cooling purposes and to remove bone chips which are generated during sawing. Due to present saw blade design, "coolant can not reach the dissection site". "It is, therefore, important to allow chip relief and to allow a cooling fluid to reach the dissection site and the dissecting tool. Proper attention to the technique will allow chip relief and the introduction of cooling irrigation, resulting in healthy, living bone which will heal readily."
In a further aspect, applicants have recognized a need to provide surgical saw blade with a hard coating bonded thereto which will protect the blade surface to thereby increase the lifespan of the blade.
In the past, applicants have attempted to coat a surgical saw blade with polytetraflurorethylene, better known by the trademark TEFLON. Experiments by applicants with TEFLON coated blades have revealed increased efficiency with marked reduction in galling. However, it was found that autoclaving as well as use of the blades in a precision slot would result in the coating stripping off and it was further discovered that chunks of coating would sometimes enter the surgical site. These chunks were very offensive to the surgical site since it was found that the TEFLON flakes were not bio-compatible with the tissues of the patients.
Applicants also experimented with ceramic coatings such as calcium phosphate and aluminum oxide. Experiments with coating surgical saw blades with these materials failed for several reasons. Firstly, the melting point of the ceramics was higher than that of the blade material and, as such, during the coating process, the temper of the blade would be destroyed. Further, it was discovered that a blade coated with ceramic could not be bent or flexed without cracking the coating.
Thereafter, experiments were conducted with combinations of methyl methacrylate and ceramics. While these combinations were superior to the TEFLON, calcium phosphate and aluminum oxide, it was found that adherence to the metallic blades was inferior. Even the milling of grooves to hold the methyl methacrylate and ceramics to the blade did not solve the problems in a satisfactory manner.
As such it was concluded from these experiments that if the blades were to be coated to improve durability thereof and consequently prevent galling, coating with a metallic alloy would have to be employed.
A need has consequently developed for a surgical saw blade which will not only be more durable in use, but which will reduce heat generation adjacent bone tissue while also allowing access of cooling and flushing water to the surgical site.
The following prior art is known to applicant:
______________________________________ U.S. Pat. No. ______________________________________ D 30,478 to Earle 864,812 to Thullier 2,670,939 to Harp 3,517,670 to Speelman 4,036,236 to Rhodes, Jr. ______________________________________
Earle discloses a grass cutting blade having a single rib extending outwardly from one face thereof. Of course, this is different from the teachings of the present invention even concerning the ribbed embodiment thereof in that the present invention contemplates ribs on opposed faces of a blade having teeth formed in a set with the ribs guiding the blade in a precision slot and with the blade coated with a metallic coating.
Thullier discloses a knife and other cutting blade in several embodiments. As the cross-sections demonstrate, each of the blades disclosed in this patent have differing cross-sectional thicknesses at different areas along the lengths thereof which would make it impossible to use these blades in conjunction with a precision slot. Furthermore, none of the embodiments of Thullier teach the use of a metallic coating bonded to the blade.
Harp discloses a mixing paddle having a plurality of rib-like structures thereon which appear to be of differing thicknesses as best seen in FIG. 4. Thus, Harp is quite distinct from the teachings of the present invention as failing to disclose a cutting blade nor a coating therefor and as not being designed for use in conjunction with a precision slot, among other reasons.
Speelman discloses a blood-letting lancet having two longitudinal ribs extending from one face thereof and a point at one or both ends thereof. The present invention is distinct from the teachings of Speelman as including in one embodiment, ribs on opposed faces of an elongated blade having teeth on opposed sides thereof, which teeth are formed in a set configuration and the further provision of a coating bonded thereto.
Finally, Rhodes teaches the concept of a surgical saw blade having teeth on one side thereof and a single elongated longitudinal rib extending outwardly from one face thereof. The lack of a plurality of ribs on opposed faces of the Rhodes, Jr. blade would inherently allow pivoting of the blade from side to side as it moves in a precision slot thus inherently damaging the tooth set.
Concerning the prior art discussed above, as pertains to one embodiment of the present invention, while ribs are disclosed in these patents in conjunction with elongated blades, the ribs are disclosed only for strengthening purposes. While the ribs of one embodiment of the present invention inherently strengthen the elongated blade, their main purpose is to provide guidance of the blade within a precision slot. This is different from the teachings of the prior art.